The effect of environmental ageing at lower and sub-zero temperatures on the adhesive joint strength

This paper examines the effect of a selected environmental ageing condition – specifically the temperature – on the strength of adhesive joints. The joint specimens were formed with EN AW 2024 aluminium alloy sheet adherends bonded with three types of epoxy resin compounds. A novelty in the research is the use of a combination of various types of epoxy resins based on Bisphenol A (BPA) and an amine curing agent dedicated for operating at lower or sub-zero temperatures. The curing conditions for all the assembled adhesive joints were identical, e.g.: temperature 24–26 °C, relative humidity 21 ± 3%, curing time 7 days. The adhesive joints were subsequently subjected to environmental ageing at lower and sub-zero temperatures (−20 °C, −15 °C, 0 °C, 5 °C). The single-lap adhesive joint specimens aged at lower and sub-zero temperatures were placed in the SH 661 temperature and humidity chamber. The reference specimens were subjected to ageing at ambient temperature in laboratory conditions. Upon completion of the ageing cycle, all adhesive joint specimens, including the reference samples, were subjected to shear strength tests on Zwick/Roell Z150 testing machine. According to DIN EN 1465 standard the testing speed was equal to 5 mm/min. The test results indicate that the adhesive joints' strength depends on a number of factors, including the environmental ones. Moreover, the type of an adhesive compound has considerable impact on the adhesive joints’ strength.